1. Field of the Invention
The present invention relates to an infrared detector; in particular, the present invention relates to a compound infrared detector in which a pyroelectric detector is combined with a thermopile detector.
2. Description of the Prior Art
As shown in FIG. 1, a known pyroelectric detector consists of a thin pyroelectric element 1 provided with electrodes 2 and 3 on both faces thereof; the electrodes 2 and 3 are connected to terminals 5 and 6 on a substrate 4 holding the thin element 1; output signals from terminals 5 and 6 are fed to a junction FET for effecting an impedance transformation; the output of the FET is then connected to an outside terminal.
As shown in FIG. 2, a known thermopile detector comprises a circular or rectangular thermopile, consisting of a first thermopile material 8 and a second thermopile material 9, constructed on a thin insulating film 7. Minute differences in the temperatures between a cold junction, fixedly mounted on the thick substrate 4 of a large capacity through said thin insulating film 7, and a central hot junction, upon which infrared rays are incident, generate signals which are fed to an outside terminal.
Although a pyroelectric detector can have a high sensitivity, it is a detector of the differential type, and as a result thereof, it provides detection signals only for sudden changes in the intensity of infrared rays; that is to say, only during sudden temperature gradients when an optical chopping means is not included.
On the other hand, although a thermopile detector can provide detection signals in accordance with slow changes in temperature, it has a relatively low sensitivity.
Although both kinds of detectors can be used in such a manner that they compensate each other by means of the suitable treatment of their signals, they cannot be placed on the identical focus of the identical optical system. For this reason, prior art using two detectors have a defect in that the number of detectors required and also the number of optical adjusting means, optical parts and the like is increased and accordingly, such a detection apparatus becomes extremely expensive as a whole.